JP7096031B2 - Board holding member - Google Patents

Description

The present invention relates to a substrate holding member, particularly a substrate holding member such as a vacuum chuck that holds a substrate such as a wafer.

In a semiconductor manufacturing apparatus, a substrate holding member is used as a member for holding a substrate such as a wafer. In such a substrate holding member, a plurality of convex portions are formed on the surface of the base, and the wafer is held by the top surface (tip surface) of the convex portions.

In order to minimize the contact area between the convex portion and the substrate, it is necessary to reduce the area of the top surface of the convex portion. Further, in order to vacuum-adsorb the substrate, the convex portion needs to have a certain height. As a result, the convex portion is formed in an elongated cylindrical shape.

Then, it has been proposed to form a film on the tip of a convex portion having an elongated cylindrical shape (see Patent Document 1). It has also been proposed to form a coating (protective layer) on the entire surface of the base (base) including the convex portion (projection), in which case the particles are prevented from falling off from the base. It is also effective (see Patent Document 2).

Japanese Patent No. 6001675 Japanese Patent No. 5063797

However, if the convex portion has an elongated cylindrical shape as in Patent Document 1, the convex portion may be damaged by the sliding force repeatedly acting on the contact surface between the convex portion and the base, and the substrate may be damaged for a long period of time. It was sometimes difficult to maintain good flatness.

On the other hand, when a protective film is formed on the entire surface of the base as in Patent Document 2, peeling or cracks occur between the substrate and the protective film after long-term use due to the difference in physical properties between the base and the protective film. There was a case. This occurs when physical properties such as linear expansion coefficient, elastic modulus, density, hardness, and crystallinity are slightly different, stress caused by the difference in expansion coefficient due to temperature change, and when the wafer is adsorbed and detached. It is thought that the stress is the cause. This stress propagates to the substrate under the protective film and causes peeling and cracking. Such peeling or cracking of the protective film may cause the generation of particles, and it may be difficult to maintain the substrate with good flatness for a long period of time.

The present invention has been made in view of the above-mentioned conventional problems, and an object of the present invention is to provide a substrate holding member capable of holding a substrate with good flatness for a long period of time.

The substrate holding member of the present invention is a substrate holding member including a base and a plurality of convex portions formed on the upper surface of the base and holding the substrate on the top surface, and the plurality of convex portions are the above-mentioned. It has a root portion extending from the upper surface of the base and a top portion formed on the root portion and including the top surface, and the plurality of convex portions are the root portion in a horizontal direction along the upper surface of the base. The cross-sectional area of the portion is larger than the cross-sectional area of the top in the horizontal direction, and at least a part of the plurality of convex portions including the top surface of the top has a young ratio as compared with the material forming the base. Is composed of a holding member formed of a large material, the holding members constituting the plurality of convex portions are separated from each other, the plurality of convex portions are continuously formed from the base, and the base is formed. It has a portion made of a material forming a table, and the material of the holding member is characterized in that the main component is the same as that of the base and the root portion .

According to the substrate holding member of the present invention, at least a part of the convex portion including the top surface in contact with the substrate is made of a holding member formed of a material having a Young's modulus larger than that of the material forming the base. This makes it possible to improve the wear resistance on the top surface in contact with the substrate and suppress the generation of particles from the top surface, as compared with the case where the convex portion is made of the same material as the base. ..

Since the cross-sectional area of the root portion of the convex portion is larger than the cross-sectional area of the top portion, the area of the apex surface is compared with the convex portion (protrusion portion) described in Patent Document 1 having the same overall cross-sectional area. Even if the above is the same, it is possible to increase the rigidity of the convex portion.

Further, since the holding members are separated from each other, the holding member is compared with the case described in Patent Document 2 in which the holding member (coating) is formed over the entire surface of the base (base). It is possible to suppress peeling and cracking.

As a result, it is possible to maintain the substrate with good flatness for a long period of time.

In the substrate holding member of the present invention, the plurality of convex portions form the root portion extending from the upper surface of the base, and are above the first convex portion having an upper end surface and the first convex portion. It is preferable that the holding member is provided with a second convex portion formed on a part of the end face and constitutes the top portion, and the holding member constitutes at least a part of the second convex portion.

In this case, since the first convex portion extends from the upper surface of the base, the first convex portion and the base can be integrally formed. As a result, it is possible to improve the adhesion between the first convex portion and the base, and it is possible to suppress the occurrence of breakage such as peeling and crack generation between them.

Further, in the substrate holding member of the present invention, it is preferable that the holding member constitutes an upper end portion including the second convex portion and at least the upper end surface of the first convex portion.

In this case, since the holding member constitutes the upper end of the second convex portion and the first convex portion, it is possible to integrally form these. As a result, it is possible to improve the adhesion between the first convex portion and the second convex portion, and it is possible to suppress the occurrence of breakage such as peeling and crack generation between them. ..

Further, since the holding member constitutes the upper end upper portion of the first convex portion, the holding member and the lower portion of the first convex portion are in close contact with each other over a wide area. Therefore, it is possible to improve the adhesion between the two, and it is possible to suppress the occurrence of breakage such as peeling and cracking between them.

Further, in the substrate holding member of the present invention, it is preferable that a recess is formed in a portion made of a material forming the base, and at least the holding member is formed in the recess.

In this case, since the concave portion is formed in the portion made of the material forming the base of the convex portion and the holding member is formed in the concave portion, the portion made of the material forming the base of the convex portion is held. It is possible to suppress the peeling of the member.

Further, in the substrate holding member of the present invention, it is also preferable that the holding member constitutes the entire of the plurality of convex portions.

In this case, since the holding member constitutes the entire convex portion, it is not necessary to form a portion continuous from the base as a part of the convex portion, so that the step of forming the convex portion becomes unnecessary and the manufacturing process is simplified. It is possible to plan.

Further, in the substrate holding member of the present invention, it is preferable that a recess is formed on the upper surface of the base, and the holding member is formed at least in the recess.

In this case, since a recess is formed on the upper surface of the base and the holding member is formed in the recess, it is possible to suppress the holding member from peeling off from the base.

The schematic sectional view of the substrate holding member which concerns on 1st Embodiment of this invention. The enlarged schematic vertical sectional view of the convex part of the substrate holding member which concerns on 1st Embodiment of this invention. An enlarged cross-sectional photograph of a convex portion of the substrate holding member according to the first embodiment of the present invention. It is an enlarged schematic vertical sectional view which shows the manufacturing process of the substrate holding member which concerns on 1st Embodiment of this invention, and shows the state which formed the holding layer on the surface of the base, and put the mask in the region. The enlarged schematic vertical sectional view of the convex part of the substrate holding member which concerns on 2nd Embodiment of this invention. The enlarged schematic vertical sectional view of the convex part of the substrate holding member which concerns on 3rd Embodiment of this invention. The enlarged schematic vertical sectional view of the convex part of the substrate holding member which concerns on 4th Embodiment of this invention. The enlarged schematic vertical sectional view of the convex part of the substrate holding member which concerns on 5th Embodiment of this invention.

The substrate holding member 1 according to the first embodiment of the present invention will be described with reference to the drawings.

As shown in the cross-sectional view of FIG. 1, the substrate holding member 1 is formed on a disk-shaped base 10 and a plurality of convex portions on the top surface 20a for holding a wafer (board) (not shown). (Protrusion, pin) 20 is provided.

In the substrate holding member 1, as shown in the partially enlarged cross-sectional view of FIG. 2, each convex portion 20 has a root portion 21 extending from the upper surface of the base 10 and a top surface 20a formed on the root portion 21. It has a top 22 including. The convex portion 20 has a cross-sectional area S1 of the root portion 21 in the horizontal direction (horizontal direction in FIG. 2) along the upper surface of the base 10 larger than the cross-sectional area S2 of the top portion 22 in the horizontal direction.

The convex portion 20 is composed of a holding member 30 in which at least a part including the top surface 20a of the top portion 22 is made of a material having a Young's modulus larger than that of the material forming the base 10. It is preferable that at least a part of the top portion 22 including the top surface 20a is made of a material having a small porosity (fewer pores) as compared with the material forming the base 10. The holding members 30 are separated from each other.

In the present embodiment, the convex portion 20 is composed of a cylindrical lower portion 23 and a cylindrical upper portion 24 that protrudes above the lower portion 23 and has a diameter smaller than that of the lower portion 23. The lower portion 23 protrudes from the surface of the base 10 and is integrally formed with the base 10, and is made of the same material as the base 10. That is, the lower portion 23 is continuously formed from the base 10.

The entire upper part 24 is composed of the holding member 30. As a result, the root portion 21 of the convex portion 20 is the root portion (lower end portion) of the lower portion 23, and the top portion 22 of the convex portion 20 is the top portion (upper end portion) of the upper portion 24.

The top surface 20a of the convex portion 20, which is the upper end surface of the holding member 30, is formed flat. The lower portion 23 corresponds to the first convex portion of the present invention, and the upper portion 24 corresponds to the second convex portion of the present invention.

The height of the lower portion 23 is preferably 0.15 to 0.35 mm, for example, 0.25 mm. The diameter of the lower portion 23 is preferably 1.0 to 1.5 mm, for example, 1.25 mm. The height of the upper portion 24 is preferably 0.02 to 0.06 mm, for example, 0.02 mm. The diameter of the upper portion 24 is preferably 0.02 to 0.2 mm, for example 0.02 mm.

In FIGS. 1 and 2, the base 10, the convex portion 20, the holding member 30, and the like are exaggerated without considering the actual shape and dimensional ratio. Therefore, it does not always match the actual shape and dimensional ratio. The same applies to FIGS. 4 to 8 described later.

Further, although it is described that both the lower portion 23 and the upper portion 24 are columnar, due to factors such as the manufacturing method, the corners are curved, the side surfaces are uneven, and the side surfaces are slanted. It does not become columnar.

Examples of the material of the base 10 and the lower portion 23 include silicon carbide (SiC) and alumina (Al2O3), but it is preferable that the base 10 is conductive and has high rigidity in order to prevent circuit destruction due to static electricity. It is preferably a silicon carbide (SiC) material sintered body. The pores of the base 10 and the lower portion 23 are preferably as small as possible because they may cause particle dusting and the like, and the porosity is 5% or less, more preferably 2% or less.

From the viewpoint of strength, it is preferable that the pore diameters of the base 10 and the lower portion 23 are small, and the average pore diameters of the base 10 and the lower portion 23 are 1 to 5 μm. For the average pore diameter, a scanning electron microscope (SEM) was used to photograph a cross section of the base 10 and the lower portion 23 magnified 2000 times, and an intercept method was used for any 30 μm square region of the obtained cross-sectional photograph. It should be calculated.

The Young's modulus (longitudinal elastic modulus) of the base 10 and the lower portion 23 is 400 to 440 GPa, more preferably 420 to 440 GPa. The Vickers hardness of the base 10 and the lower portion 23 is 22 to 26 GPa (load 0.5 kgf).

Examples of the material of the holding member 30 include silicon carbide (SiC) and alumina (Al2O3), but it is preferable that the main component is the same as that of the base 10 and the lower portion 23, and it is preferable that the holding member 30 is made of silicon carbide. The number of pores in the holding member 30 is preferably smaller because it includes a portion that comes into direct contact with a substrate such as a wafer. The porosity of the holding member 30 is smaller than the porosity of the base 10 and the lower portion 23, and is 1% or less, more preferably 0.5% or less. The Young's modulus of the holding member 30 is larger than the Young's modulus of the base 10 and the lower portion 23, and is 450 to 480 GPa, more preferably 460 to 480 GPa. Here, the Young's modulus of the holding member 30, the base 10, and the lower portion 23 can be measured according to ISO 14577, which is a test method using the nanoindentation method. The Vickers hardness of the holding member 30 is 28 to 31 GPa (load 0.5 kgf).

When the material of the base 10 and the lower portion 23 is a silicon carbide sintered body, it is preferable that the holding member 30 is made of silicon carbide formed by a thermal CVD (chemical vapor deposition) method. According to the thermal CVD method, the holding member 30 has very few pores, no pores are observed in the SEM observation of the cross section enlarged 2000 times as large as that of the holding member 30, and the porosity of the holding member 30 is substantially high. This is because the porosity and Young's modulus are easily set to 0% within the above-mentioned ranges, and the thickness of the holding member 30 can be easily increased to about 1 mm.

FIG. 3 shows a scanning electron microscope in which a holding member 30 made of SiC is formed on a lower portion 23 obtained by normal-pressure sintering of SiC to which B4C and C are added as sintering aid components by a thermal CVD method. It is an enlarged cross-sectional photograph using (SEM). In the silicon carbide sintered body of the lower portion 23, constant pores are distributed, whereas no pores are observed in the holding member 30 made of SiC formed by the thermal CVD method, and the porosity is substantially 0. It is confirmed that it is%. The number of pores and the porosity of the holding member 30, the base 10 and the lower portion 23 can be evaluated by observing an enlarged cross-sectional photograph using an SEM.

The case where the lower portion 23 and the upper portion 24 have a cylindrical shape, respectively, has been described, but the present invention is not limited to this as long as the cross-sectional area S1 of the root portion 21 of the convex portion is larger than the cross-sectional area S2 of the top portion 22. For example, the lower portion 23 and the upper portion 24 may each have a truncated cone shape, or the lower portion 23 and the upper portion 24 may have a truncated cone shape as a whole. Further, the shape of the lower portion 23 and the upper portion 24 may be any shape as long as it spreads from the top to the bottom, and may be a prism, a truncated cone, a truncated cone, or the like, in addition to being cylindrical. Further, at least one of the upper portion 24 or the lower portion 23 may have a shape in which a plurality of cylindrical shapes, truncated cone shapes, and the like are stacked in the vertical direction.

In the substrate holding member 1, the wafer is supported by the substrate holding member 1 so as to abut on each top surface 20a of the plurality of convex portions 20. Then, for example, although not shown, the air in the space defined by the substrate holding member 1 and the wafer is removed by a vacuum suction device such as a vacuum pump (not shown) connected to the vacuum suction path 11 formed on the base 10. By being sucked, the wafer is sucked and held by the substrate holding member 1 by this suction force.

Next, a method of manufacturing the substrate holding member 1 will be described with reference to FIG.

First, a substantially disk-shaped molded body made of silicon carbide is produced, and the molded body is sintered at 1900 to 2100 ° C. in an Ar gas atmosphere to produce a substantially disk-shaped silicon carbide sintered body. A carbon-containing substance such as B4C or C may be added to the silicon carbide powder material as a sintering aid component.

Next, the upper surface of the silicon carbide sintered body is subjected to grinding, blasting, electric discharge machining, grindstone machining, high-energy beam irradiation processing such as a laser beam, and the like to remove the lower portion 23 of the plurality of convex portions 20. Form.

Further, for example, the holding layer 40 made of silicon carbide is formed by a thermal CVD method, a plasma CVD method, an ion plating method, or the like so as to cover the upper surface of the base 10 over the entire surface including the surface of the lower portion 23. .. The holding layer 40 is preferably formed by a thermal CVD method, but if the porosity and Young's modulus of the holding layer 40 can be within the range of the holding member 30 described above, a plasma CVD method or ion plating can be used. It may be done by a method such as a law. The holding layer 40 formed in this way covers the entire surface of the upper surface of the base 10 and the surface of the lower portion 23.

Next, the mask M is installed so as to cover the region of the upper portion 24, and the holding layer 40 is removed by performing blasting or the like on the region excluding the region covered with the mask M. The holding layer 40 may be removed by grinding, electric discharge machining, grindstone machining, high energy beam irradiation machining such as laser beam, or the like. As a result, the holding layer 40 remains in the portion to be the upper portion 24, and the holding member 30 is formed. Further, the top surface of the holding member 30 is polished so that at least the top surface of the convex portion 20 is flat.

According to the substrate holding member 1 described above, at least a part of the convex portion 20 including the top surface 20a in contact with the wafer has a smaller porosity (fewer pores) than the material forming the base 10. It is composed of a holding member 30 made of a material having a large Young's modulus. As a result, the wear resistance on the top surface 20a in contact with the wafer is improved and the generation of particles from the top surface 20a is suppressed as compared with the case where the convex portion 20 is made of the same material as the base 10. Is possible.

Since the cross-sectional area S1 of the root portion 21 is larger than the cross-sectional area S2 of the top portion 22, the convex portion 20 has the same overall cross-sectional area as the elongated cylindrical convex portion (projection) described in Patent Document 1. By comparison, even if the area of the top surface 20a is the same, it is possible to increase the rigidity of the convex portion 20.

Further, since the holding members 30 are separated from each other, the holding member (coating) is held over the entire surface of the base (base) as compared with the case described in Patent Document 2. It is possible to suppress peeling and cracking of the member 30.

As a result, it is possible to maintain the wafer with good flatness for a long period of time.

Further, since the lower portion 23 extends from the upper surface of the base 10, the lower portion 23 and the base 10 can be integrally formed. As a result, it is possible to improve the adhesion between the lower portion 23 and the base 10, and it is possible to suppress the occurrence of breakage such as peeling and crack generation between them.

Next, the substrate holding member 1A according to the second embodiment of the present invention will be described with reference to the drawings. As shown in FIG. 5, the substrate holding member 1A differs from the substrate holding member 1 described above in that the holding member 30A is also formed in the recess 23Aa formed on the upper surface of the lower portion 23A. do.

As a result, the holding member 30A is formed in a shape in which the portion formed in the recess 23Aa of the lower portion 23A and the entire upper portion 24 are integrated. The cross-sectional shape of the recess 23Aa in the vertical direction is not particularly limited to a semicircular shape, a semi-elliptical shape, a rectangular shape, or the like, and may be a shape in which the inside is enlarged to the side as compared with the opening. The recess 23Aa preferably has a depth of 0.01 to 0.2 mm and a width of the opening of 0.02 to 0.2 mm.

When the lower portion 23A is formed, such a holding member 30A forms a recess 23Aa on the upper surface of the lower portion 23A by performing grinding, blasting, electric discharge machining, grindstone machining, high energy beam irradiation, and the like. It may be formed so as to form the holding layer 40 with.

According to the substrate holding member 1A described above, it is possible to maintain good flatness of the wafer for a long period of time, similarly to the substrate holding member 1 described above.

Further, since the recess 23Aa is formed on the upper surface of the lower portion 23A made of the material forming the base 10A of the convex portion 20A and the holding member 30A is formed in the recess 23Aa, the holding member 30A is formed from the lower portion 23A. It is possible to suppress peeling.

Next, the substrate holding member 1B according to the third embodiment of the present invention will be described with reference to the drawings. As shown in FIG. 6, the substrate holding member 1B is made of the same material as the upper portion 24B in which the upper portion of the lower portion 23B constitutes a part of the holding member 30B as compared with the substrate holding member 1 described above. Only that is different.

As a result, the holding member 30B is formed in a shape in which the upper portion of the lower portion 23B and the entire upper portion 24B are integrated. The lower portion of the lower portion 23A is continuously formed from the base 10. The thickness of the upper part of the lower part 23B of the holding member 30B is preferably 0.01 to 0.2 mm.

According to the substrate holding member 1B described above, it is possible to hold the wafer with good flatness for a long period of time, similarly to the substrate holding member 1 described above.

Further, since the holding member 30B constitutes the upper end upper portions of the upper portion 24B and the lower portion 23B, these can be integrally formed. As a result, it is possible to improve the adhesion between the lower portion 23B and the upper portion 24B, and it is possible to suppress the occurrence of breakage such as peeling and crack generation between them.

Further, since the holding member 30B constitutes the upper end portion of the lower portion 23B, the holding member 30B and the lower portion of the lower portion 23B are in close contact with each other in an area wider than the cross section of the upper portion 24B. Therefore, it is possible to improve the adhesion between the two, and it is possible to suppress the occurrence of breakage such as peeling and cracking between them.

Next, the substrate holding member 1C according to the fourth embodiment of the present invention will be described with reference to the drawings.

As shown in FIG. 7, the substrate holding member 1C is different from the substrate holding member 1 described above in that the entire convex portion 20C is composed of the holding member 30C. The convex portion 20C has a truncated cone shape as a whole, unlike the convex portion 20. Further, the shape of the convex portion 20C may be a shape that spreads from the top to the bottom, and is not only a truncated cone shape but also a truncated cone and a side surface that is convex or concave toward the outside. It may have a shape similar to a truncated cone having a curved surface.

The height of the convex portion 20C is preferably 0.15 to 0.35 mm, for example, 0.25 mm. The diameter of the root portion 21C of the convex portion 20C is preferably 0.2 to 1.5 mm, for example, 0.25 mm. The diameter of the top portion 22C of the convex portion 20C is preferably 0.02 to 0.2 mm, for example, 0.05 mm.

Since it is not necessary to form the lower portion 23 of the holding member 30C as in the case of manufacturing the substrate holding member 1 described above, the step of forming the lower portion becomes unnecessary, and the manufacturing process can be simplified. It will be possible.

If the holding member 30C having a truncated cone shape is formed by forming the holding layer 40 so as to cover the entire upper surface of the base 10C and removing the holding layer 40 other than the portion serving as the holding member 30C. good. It is particularly preferable to remove the holding layer 40 by laser beam processing that does not involve air flow in the processing. In processing involving the flow of powder such as blasting, a curved surface is formed between the lower portion of the holding member 30C having a truncated cone shape and the base 10C. However, in laser beam processing, the formation of such a curved surface can be suppressed.

According to the substrate holding member 1C described above, it is possible to hold the wafer with good flatness for a long period of time, similarly to the substrate holding member 1 described above.

Next, the substrate holding member 1D according to the fifth embodiment of the present invention will be described with reference to the drawings.

As shown in FIG. 8, the substrate holding member 1D has only the holding member 30D formed in the recess 10Da formed on the upper surface of the base 10D as compared with the substrate holding member 1C described above. It's different.

As a result, the holding member 30D is configured to have a shape in which the portion formed in the concave portion 10Da of the base 10D and the convex portion 20D are integrated. The vertical cross-sectional shape of the recess 10DAa is not particularly limited to a semicircular shape, a semi-elliptical shape, a rectangular shape, or the like, and may be a shape in which the inside is enlarged to the side as compared with the opening. The recess 10Da preferably has a depth of 0.01 to 0.2 mm and a width of the opening of 0.02 to 0.2 mm.

Such a recess 10Da is formed by forming a base 10 having a flat upper surface and then performing grinding, sandblasting, electric discharge machining, grindstone machining, high energy beam irradiation such as a laser beam, and the like to form the upper surface of the base 10D. A recess 10Da may be formed in the recess.

According to the substrate holding member 1D described above, it is possible to hold the wafer with good flatness for a long period of time, similarly to the substrate holding member 1 described above.

Further, since the holding member 30D is formed in the recess 10Da formed on the upper surface of the base 10D, it is possible to suppress the holding member 30D from peeling off from the base 10D.

1,1A, 1B, 1C, 1D ... Substrate holding member, 10,10A, 10B, 10C, 10D ... Base, 10Da ... Recessed, 11 ... Vacuum suction path, 20, 20A, 20B, 20C, 20D ... Convex , 20a, 20Aa, 20Ba, 20Ca, 20Da ... top surface, 21,21A, 21B, 21C, 21D ... root part, 22, 22A, 22B, 22C, 22D ... top, 23, 23A, 23B ... bottom (first) Convex part), 23Aa ... concave part, 24, 24A, 24B ... upper part (second convex part), 30, 30A, 30B, 30C, 30D ... holding member, 40 ... holding layer, M ... mask.

Claims (6)

A substrate holding member having a base and a plurality of protrusions formed on the upper surface of the base and holding the board on the top surface.
The plurality of convex portions have a root portion extending from the upper surface of the base and a top portion formed on the root portion and including the top surface.
In the plurality of convex portions, the cross-sectional area of the root portion in the horizontal direction along the upper surface of the base is larger than the cross-sectional area of the top portion in the horizontal direction.
The plurality of convex portions are made of a holding member in which at least a part including the top surface of the top is made of a material having a Young's modulus larger than that of the material forming the base.
The holding members constituting the plurality of convex portions are separated from each other.
The plurality of convex portions are continuously formed from the base and have a portion made of a material forming the base.
The material of the holding member is a substrate holding member whose main component is the same as that of the base and the root portion . The plurality of convex portions form the root portion extending from the upper surface of the base, and are formed on a first convex portion having an upper end surface and a part of the upper end surface of the first convex portion. And with a second convex portion constituting the top
The substrate holding member according to claim 1, wherein the holding member constitutes at least a part of the second convex portion. The substrate holding member according to claim 2, wherein the holding member constitutes an upper end portion including the second convex portion and at least the upper end surface of the first convex portion. The invention according to any one of claims 1 to 3, wherein a recess is formed in a portion made of a material forming the base, and at least the holding member is formed in the recess. Board holding member. The substrate holding member according to any one of claims 1 to 3, wherein the holding member constitutes the entire of the plurality of convex portions. A recess is formed on the upper surface of the base.
The substrate holding member according to claim 5, wherein the holding member is formed at least in the recess.

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